The field of the present invention is chain belts for V pulleys, especially, V pulleys used in stepless speed change transmissions for heavy vehicles.
A general example of a stepless speed change transmissions for heavy vehicles in shown in FIG. 1 consisting of a pair of V pulleys with an endless chain belt wrapped around these pulleys to transmit a drive force from one pulley to the other.
As shown in FIG. 2 and FIG. 3 this chain belt 1 is made of chain links each of which have a protruding section to form a Y shape. There is a main link plate 2 and sub-link plate 3 and both these plates have holes 2a and 3a formed in them at the same pitch. These plates are interleaved so that the holes line up and into these holes are inserted rocker pins 4 and 5 to provide a curved contact face to connect the link plate 2 and sub-link plate 3 together so that they can move freely rotatably to each other. In the protruding section of the link plates 2 are holes to take a drive block 6 which fits tightly into the holes to form a single body with the respective pair of link plates.
The plurality of sub-link plates 3 are positioned between the main link plates 2 with their respective holes 3a lining up with the holes 2a in the main link plates so as to make up No. 1 unit A assembly as shown in FIG. 3. A No. 2 unit B assembly is made up similarly but with one sub-link plate less than the No. 1 unit A assembly, so as to fit between the No. 1 unit A assembly. These No. 1 unit A and No. 2 unit B assemblies are arranged alternately and slid together to intermesh. Then rocker pins 4 and 5 are fitted in holes 2a and 3a respectively of link plates 2 and 3 to connect the link plates together.
The rocker pins 5 are inserted in the respective holes 2a of No. 1 unit A with their contact surfaces facing towards each other and rocker pins 4 are inserted in the respective holes 3a of No. 2 unit B with the contact surfaces facing each other so that the contact faces of rocker pin 5 and rocker pin 4 contact each other when the units are assembled together with the sub-link plates 3. By this arrangement the endless chain is formed as shown in FIG. 2 with No. 1 units A and No. 2 units B alternating.
The rocker pins 4 and 5 are fitted in holes 2a and 3a, but so that the internal faces coincide correctly, relative rotation is restricted. However, link plates 2 and 3 are able to pivot relative to each other. Further the contact faces of rocker pins 4 and 5 are maintained in the link plates 2 and 3 so that they contact at the central position with respective units A and B arranged in a straight line. Also, the drive block 6 is kept inside of the chain line L formed by the connections of rocker pins 4 and 5, as shown in FIG. 1. Consequently when the chain belt wraps around V pulley P this drive block 6 contacts at a smaller diameter than that of the chain line L.
With the chain belt 1 constructed in this way and wrapped around V pulleys P as shown in FIG. 1 the drive block 6, as shown in FIG. 3, contacts the transmission drive face of V pulley P at both ends and by the friction of contact, drive force is transmitted from one V pulley P to the other V pulley P. Also by changing the contact radius between the drive blocks and the respective V pulleys P, stepless speed change between the two V pulleys P can be achieved.
A problem with this arrangement of chain belt is that, when the chain belt wraps around the V pulley P, a drive sound is generated resulting in an undesirable condition. The cause of this sound is considered to be due to the following phenomena.
When the speed change is at a fixed condition, the chain belt 1 speed is fixed. Considering the chain line L between the respective V pulleys P, the speed of drive block 6 is the same as that of chain line L (This drive block is shown as 6a in the schematic diagram of FIG. 4). However, as shown in FIG. 4, when this drive block wraps around V pulley P (shown as 6b in FIG. 4), the drive block speed changes to Vb due to the differences between the contact point radius RB of drive block 6 and the radius to the chain line L. In this example, since drive block 6 is a distance S inside the chain line L the speed Vb is less than V. This change in speed results in an impact which is considered to give rise to the drive sound and this is supported by the results of an experiment illustrated in FIG. 5 showing the relation between the relative speed of chain line L and drive block 6b and the drive sound. Accordingly, to reduce this drive sound in stepless speed change transmissions using the chain belt 1, it is necessary to keep the relative speed of chain line L and drive block 6b as small as possible. This is one of the problems that this invention is aimed at solving.
A further problem is that, with previously constructed chain belts, the drive block 6b has been of a rectangular shape resulting in stress concentrations occurring at the contact area between the drive block and the main link plate 2. To reduce these stress concentrations a cylindrical shaped drive block 8 fitted into circular holes 9 in the respective link plates 2 and 3 as shown in FIG. 6 has been considered. However, with a cylindrical shaped drive block 8 it is difficult to ensure correct alignment during assembly of the contact end angles of the drive blocks 8a which are cut at an angle to mate with the inner contact faces of the V pulleys P. This makes manufacture and assembly of the chain belt difficult.